A ‘tripledemic’? Flu and other infections return as COVID-19 cases rise
By Apoorva Mandavilli
For more than two years, shuttered schools and offices, social distancing and masks granted Americans a reprieve from flu and most other respiratory infections. This winter is likely to be different.
With few to no restrictions in place and travel and socializing back in full swing, an expected winter rise in COVID-19 cases appears poised to collide with a resurgent influenza season, causing a so-called twindemic” — or even a tripledemic, with a third virus, respiratory syncytial virus, or RSV, in the mix.
Cases of flu have begun to tick up earlier than usual and are expected to soar over the coming weeks. Children infected with RSV (which has symptoms similar to those of flu and COVID-19), rhinoviruses and enteroviruses are already straining pediatric hospitals in several states.
“We’re seeing everything come back with a vengeance,” said Dr. Alpana Waghmare, an infectious diseases expert at Fred Hutchinson Cancer Center and a physician at Seattle Children’s Hospital.
Most cases of COVID-19, flu and RSV are likely to be mild, but together they may sicken millions of Americans and swamp hospitals, public health experts warned.
“You’ve got this waning COVID immunity, coinciding with the impact of the flu coming along here, and RSV,” said Andrew Read, an evolutionary microbiologist at Penn State University. “We’re in uncharted territory here.”
RSV causes about 14,000 deaths among adults 65 and older and up to 300 deaths among children younger than 5 each year. No vaccine is available, but at least two candidates are in late-stage clinical trials and appear to be highly effective in older adults. Pfizer is also developing an antiviral drug.
Another COVID-19 wave?
Coronavirus cases are low but are beginning to rise in some parts of the country. Several European countries, including France, Germany and Britain, are experiencing an uptick in hospitalizations and deaths, prompting experts to worry that the U.S. will follow suit, as it has with previous waves.
Some of the coronavirus variants that are picking up momentum are adept at dodging immunity and drugs such as Evusheld and Bebtelovimab, which are especially important for protecting immunocompromised people.
People with weakened immune systems “remain at risk even despite getting all of the recommended or even additional doses of vaccine,” Waghmare said.
Public health experts are particularly concerned about a constellation of omicron variants that seem to dodge immunity from the vaccines and even from recent infection better than previous variants did.
The latest booster vaccines made by Pfizer and Moderna were designed for the variants that dominated this past summer but not for these newer variants. Still, they raise antibody levels overall, and should help stave off severe symptoms and abridge the duration of illness, said Aubree Gordon, an public health researcher at the University of Michigan.
The BA.5 variant was the most immune-evasive variant until recently, but it is rapidly being replaced by others, including two that show an even greater ability to sidestep immunity.
One of them, known as BQ.1.1, is the leading candidate for causing a winter wave, and it has already sent cases soaring in Europe. Although it and a closely related variant called BQ.1 together account for only about 11% of cases in the United States, their share has grown rapidly from just 3% two weeks ago.
A combination of two omicron subvariants called XBB has been fueling a wave of cases in Singapore, among the most highly vaccinated nations in the world. Its subvariant XBB.1 has just arrived in the United States. Another variant, called BA.2.75.2, is also highly immune evasive and causes more severe disease, but is so far responsible for less than 2% of cases nationwide.
Sign of a bad flu season
Before the coronavirus walloped the world, flu viruses sickened millions each winter, and killed tens of thousands of Americans. In the 2018-19 season, the flu was responsible for 13 million medical visits, 380,000 hospitalizations and 28,000 deaths.
Flu season in the Southern Hemisphere, typically between May and October, is highly predictive of winters in the Northern Hemisphere. This year, flu began weeks earlier than usual in Australia and New Zealand, and the numbers of cases and hospitalizations were markedly higher.
Gordon tracks influenza rates among children in Nicaragua, which has a flu season spanning June and July, and a larger one in the late fall. More than 90% of the population was considered fully vaccinated against COVID-19 by last January, and many people had also gained immunity from one or more infections.
Still, the country saw high rates of both COVID-19 and influenza in the first half of this year. Influenza rates among children were higher than in the 2009 flu pandemic, and the children were sicker on average than in previous years. “We saw a lot of hospitalizations,” Gordon said.
In the United States, flu typically begins to pick up in October and runs through March, peaking sometime between December and February. But in some states, the season is already underway.
About 3% of tests nationwide were turning up positive for flu as of Oct. 8, according to the Centers for Disease Control and Prevention, but the rates are higher than 10% in some Southeastern states and higher than 5% in the South Central region. In Texas, the proportion of tests positive for flu jumped to 5.3% in early October from 3.7% the week before.
Some communities are at increased risk of severe illness and hospitalization for flu. During flu seasons from 2009-22, rates of hospitalization were 80% higher among Black adults, 30% higher among American Indian/Alaska Native adults and 20% higher among Hispanic adults compared with white adults, according to a CDC report released last week.
Yet, flu vaccination rates were much lower in these groups. Vaccine coverage also declined by about 9 percentage points from the previous year in pregnant women across all racial and ethnic groups.